Semiconductor (silicon chip) storage.
(a) More recent developments have led to the use of semiconductors
in primary storage units. Semiconductor memory is composed of circuitry on silicon
chips. One silicon chip, only slightly bigger than one core, can hold as much as
thousands of cores. The speed of processing with semiconductors is also significantly
(b) Semiconductors are designed to store data in locations called bit
cells, which are capable of being either "on" or "off." Bit cells are arranged so that they
can be written to or read from, as needed. They can be accessed directly, rather than
having to go through all the memory in sequence. This is referred to as random access
memory (RAM); a concept introduced in Lesson 1. Another term for this is direct
access, covered later in this lesson. (See para 2-Bc.)
(c) Final results remain in the core memory until the control unit causes
them to be erased, normally after the results are transferred to an output device. After
all computations and manipulations are completed, the results are recorded in
peripheral memory, which takes the form of magnetic tape or disk.
Figure 2-9. Relationship of peripheral input-output devices and memory to the CPU.
d. Control Unit. The control unit is the most crucial element of the computer. It
does not process or store data. Rather, it directs the overall functioning of the other
units and controls data flow. It interprets the instructions of a program in storage and
produces signals. These signals act as commands to circuits directing them to execute
the instructions. In addition, the control unit communicates with the input and output
devices to initiate the transfer of data, instructions, and results to and from storage.